A phenolic resin has been used, for example, as a curing agent for epoxy resins, and an epoxy resin composition which is cured by a phenolic resin as a curing agent is widely used in electrical and electronic fields such as a semiconductor sealing material and a printed circuit board insulating material from the viewpoint that the cured product has excellent heat resistance and moisture resistance, in addition to an adhesive, a molding material, and a coating material.
Among these, a power semiconductor represented by a power module for an automobile is a technology crucial to energy saving in electrical and electronic equipment, and with a larger current, miniaturization, and high efficiency of a power semiconductor, transition from a silicon (Si) semiconductor in the related art to a silicon carbide (SiC) semiconductor has been advancing. The advantage of the SiC semiconductor is that the SiC semiconductor can be operated under higher temperature conditions, and therefore, a semiconductor sealing material is required to have higher heat resistance than those of semiconductor sealing materials in the related art. In addition, it is also important for the required performance of a semiconductor sealing resin to exhibit high flame retardancy without using a halogen-based flame retardant, and a resin material which has such performance has been required.
As the resin material to cope with these various required characteristics, for example, the phenolic resin represented by the following structural formula is known (refer to PTL 1).

Such a phenolic resin exhibits excellent flame retardancy in terms of the cured product; however, does not have sufficient heat resistance.